The present invention relates to a rare-earth borate, to a precursor thereof, to processes for their preparation and to the use of this borate as a luminophore.
The fields of luminescence and electronics are currently experiencing a period of considerable development. As an example of such development, mention may be made of the improvement of plasma systems (screens and lamps) for novel visualization and lighting techniques. One concrete application is that of the replacement of current television screens with flat screens. These novel applications require luminophoric materials having increasingly enhanced properties. Thus, besides their luminescent property, specific characteristics of morphology or of particle size are required of these materials in order to facilitate, in particular, their use in the desired applications.
More precisely, there is a requirement for luminophores having a narrow particle size distribution and, optionally, in the form of micron-sized individualized particles.
The main object of the invention is to afford products having such particle size characteristics.
Another object of the invention is to afford luminophores having enhanced luminescent properties.
A third subject of the invention is a preparation process which makes it possible to obtain products having these characteristics directly.
With this aim, the rare-earth borate of the invention is characterized in that it is in the form of cubic, parallelepipedal or spherical particles and in that it has a dispersion index of not more than 0.8.
By way of borate precursor, the invention also relates to a rare-earth boron hydroxycarbonate, characterized in that it is in the form of cubic, parallelepipedal or spherical particles and in that it has a dispersion index of not more than 0.8.
As other product, the invention moreover relates, by way of borate precursor, to an yttrium boron hydroxycarbonate also comprising terbium, this compound having luminescent properties.
The invention also covers a process for the preparation of a rare-earth boron hydroxycarbonate, characterized in that a rare-earth carbonate or hydroxycarbonate is reacted with boric acid, the reaction medium being in the form of an aqueous solution.
The invention moreover covers a process for the preparation of a rare-earth borate, characterized in that a rare-earth carbonate or hydroxycarbonate is reacted with boric acid, the reaction medium being in the form of an aqueous solution, and the reaction product is calcined.